1. Field of the Invention
The present invention relates to the removal of oil pollution from surface waters and more particularly the invention relates to the method and equipment for the clean-up of oil slicks on surface waters.
2. Description of the Prior Art
The frequency and danger of oil spills has greatly increased in the past several years due to the use of supertankers and the off-shore drilling in geologically active areas. Oil spill disasters have been experienced in the last several years due to these activities.
The techniques available for controlling and removing the slick from surface waters are unsatisfactory. Dispersants and detergents are effective in eliminating much of the slick but are feared because of the unknown effect on the ecological balance. Various absorbent materials have proposed to be applied to the slick to sink the oil to the bottom of the ocean. Again, this may drastically upset the ecological balance.
Another technique utilizes a treated silica which will act as a wick and permit burning of the slick. This is not effective in many circumstances and is dangerous, especially in the presence of a natural gas leak. For these reasons, the slicks have been mainly controlled by very primitive methods such as by skimming with pumps and by coagulating the oil with straw which is then removed and burned.
The containment, removal, and cleanup of spilled oil are among the most difficult and most misunderstood problems in ocean engineering. The present difficulties are both technological (because physical and chemical understanding of some of the phenomena is incomplete) and sociological (because many untrained people wrongly believe that the problem is simple enough to be solved in short order with present-day technology). Except in a few highly specialized areas-offshore oil well drilling among them-business and government have devoted far less capital expenditure to ocean engineering than to other fields in the sense that many potential areas for technological development have not been pursued to the extend possible. The containment, removal, and cleanup of spilled oil is one such area. The application of modern technology to this problem did not begin on any large scale until the aftermath of the Torrey Canyon disaster in 1967.
There are many reasons why oil spill cleanup problems are so difficult. There is a lack of understanding of the physics and chemistry underlying some of the pollution control difficulties. Some oil slicks cover tens of square miles. Currents and waves generate enormous forces on equipment. The logistics of dealing with something so large and so mobile in the face of the large forces of the sea are staggering. The area of the earth susceptible to an oil spill is large, and spills occur at random.
A number of materials have been used to remove or reduce oil slicks. Treating agents have been used to deal with accidents and field and laboratory experiments have been done to assess their usefulness and to develop the technology to use them. The types of agents which have been used to date are:
1. Dispersants -- chemicals forming oil-in-water suspensions;
2. Sinking agents -- materials that mix with the oil and create a mixture dense enough to sink;
3. Burning agents -- material put on the slick to assist ignition or enhance combustion of spilled oil;
4. Biodegradants -- substances that promote oxidation of oil by microbial action;
5. Gelling agents -- chemicals that form semi-solid oil agglomerates to facilitate removal;
6. Herding agents -- chemicals that concentrate the spilled oil in a small area;
7. Sorbents -- materials that absorb or adsorb oil to form a floating mass for later collection and removal.
Dispersants are chemical compounds that act to enhance the surface spreading of oil slicks and to emulsify the oil into the water beneath it. These effects increase the surface area of the slick so that more of it is susceptible to biodegradation. When emulsification (breaking the oil into very small droplets that become mixed with the water) occurs, the slick disperses vertically as well as horizontally. Toxicity of dispersed slicks is a major problem and is due both to the effect of the dispersant and to the increased oil surface to which marine organisms are exposed.
The use of chemical dispersants presents two major problems. The first is to obtain adequate mixing between the dispersant and the oil slick; and the second is to minimize toxicity to marine life. The mixing difficulty was demonstrated in the Santa Barbara accident, where it was found that after the dispersant was spread in a fine mist over the oil slick, it was necessary to run work boats through the slick so that their propeller action would mix the dispersant with the oil. Work is currently underway on the development of dispersants that will require little or no mixing. However, the question of toxicity remains. Some dispersants are more toxic to marine life than others, and the differences may relate in part to varying quantities of oil surface to which organisms are exposed. As oil slicks are dispersed into droplets, the surface area multiplies.
A less serious problem with dispersants involves the stability of the oil-water emulsion they generate. Experiments have shown that with some dispersants the lifetime of this emulsion can be relatively short, and the dispersed oil soon recombines into a slick. However, the stability of the emulsion generated by other dispersants is quite long, and a number of companies are doing work on increasing the emulsion stability.
Dispersants have been found effective when it is advantageous to disperse small parts of an oil slick. For example, dispersants were used and found effective to remove slicks in the vicinity of the burning oil platform at the Chevron Oil spill. However, it would have been impossible, even if allowed by law, to completely disperse all the polluting oil from this incident. If dispersants requiring no mixing are developed in the future, it may become possible to disperse an entire slick of moderate size.